JP3310818B2 - Evaluation method for remaining life of Ni-base heat-resistant alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the remaining life of a Ni-base heat-resistant alloy used for a gas turbine blade or the like.

[0002]

2. Description of the Related Art Conventional methods for estimating the metal use temperature of a Ni-base heat-resistant alloy include a γ ′ phase standard photograph of a material having a known heating temperature and time, and a γ of a material whose metal temperature is to be estimated. 'Compared with a phase photograph, a skilled person semi-quantitatively judges changes in the metal structure (such as coarsening of the γ' phase), but there is still no method for estimating the creep rupture life ratio from the γ 'phase. Not established.

[0003]

The conventional method is a technique which can be judged only by a skilled person, and its use is limited. In addition, there is a problem that it is difficult to express quantitative accuracy due to poor objectivity. Accordingly, the present invention is intended to solve the above-mentioned problems and to provide a method for evaluating the remaining life of a Ni-based heat-resistant alloy that can prevent a metal operating temperature or a creep rupture before it occurs.

[0004]

The present invention makes it possible to solve the above-mentioned problems by employing the following constitution. (1) A method for evaluating the remaining life of a Ni-base heat-resistant alloy, which comprises estimating a creep rupture life ratio by detecting a rafting ratio of a γ ′ phase of a metal structure in the Ni-base heat-resistant alloy.

(2) For a Ni-base heat-resistant alloy sample whose temperature and time history is known, the equivalent circle diameter of the γ '
Mirror parameter [LMP = (T + 273) (C + 1)
ogt)] and a circle-equivalent diameter are determined in advance, and the metal temperature T is determined from the circle-equivalent diameter of the γ 'phase of the Ni-base heat-resistant alloy to be evaluated.
The remaining life evaluation method of the described Ni-base heat-resistant alloy.

(3) A stress is applied to the Ni-base heat-resistant alloy sample to be evaluated, and the major axis and minor axis of the γ 'phase are measured on a plane parallel to the loading direction (stress-loaded plane) and a plane perpendicular to the loading direction (stress-free plane). And the aspect ratio of each surface (major axis / minor axis)
And the raft ratio Φ (aspect ratio of the stress-loaded surface / aspect ratio of the surface without stress) is determined, and the creep rupture life ratio ( (2) The method for evaluating the remaining life of a Ni-base heat-resistant alloy according to the above (2), wherein a hysteresis time t / creep rupture life tr) is obtained.

[0007]

The present inventors have noticed that the γ 'phase is elongated (rafted) when a Ni-based heat-resistant alloy is used at a high temperature for a long time at a high temperature under a stress load.
This was measured at a high magnification of about 5000 times using EM), and the Larson-Miller parameter [LMP = (T + 2)
73) × (C + logt)], a rapid and objective quantitative evaluation of the creep rupture life ratio was successfully achieved.

That is, for a material having a known temperature / time history, the change of the γ ′ phase is measured by an SEM in advance to prepare a calibration curve for the average value d of the circle equivalent diameter and the LMP,
The metal use temperature is estimated by applying the γ 'phase to be evaluated. The average value d of the circle-equivalent diameter of the γ ′ phase is also determined for the plane parallel to the plane perpendicular to the stress load direction of the γ ′ phase, and the change is arranged by LMP [= (T + 273) × (C + logt)]. Estimate the metal temperature T.

Next, the ratio α (aspect ratio = a / b) of the minor axis b to the major axis a of the γ ′ phase is determined by an image processing apparatus, and the aspect ratio ασ (a ′ / b ′) in the direction of receiving a stress load is obtained.
And the no-load aspect ratio α ₀ (a / b) was determined as the raft ratio Φ. Φ = ασ / α ₀ = (a ′ / b ′) / (a / b) Then, the relationship between Φ and LMP for each temperature and time is estimated, and Φ
And LMP that agree with each other is estimated from the relationship of Φ-LMP, and the creep rupture life ratio t / tr is estimated.

[0010]

1 to 3 show the change in the γ 'phase of a Ni-base heat-resistant alloy. FIG. 1 shows the angular γ' phase of a material. This material undergoes a temperature and time history with a Larson-Miller parameter (LMP) of 29.26 × 10 ³ to be rounded and coarse as shown in FIG. Further, the temperature / time history is added, and
When a stress of ² kgf / mm ² is applied, the γ ′ phase is further coarsened and elongate (raft) as shown in FIG.

FIG. 4 is a d- LMP diagram showing an example of a calibration curve of the change (coarsening) of the average value d of the circle equivalent diameter of the γ ′ phase. There is no influence of stress, and it can be expressed by equation (1). LMP = 8.03 · log d +29.18 (1) where LMP = (T + 273) (20 + logt) × 1
0 ^-3 T: Temperature during history (° C.) t: History time (hr) d : Average value of equivalent circle diameter of γ ′ phase (μm) (However, constant C may be changed for each alloy, In the above formula, it was 20)

FIG. 5 shows the history time t and the creep rupture time tr with respect to the change in the aspect ratio (major axis / minor axis) of the γ ′ phase.
Is an example of the relationship of the following Φ (ασ / α ₀ ) to the creep rupture life ratio (t / tr) of the ratio. As is clear from the figure, as the creep rupture life ratio increases,
The aspect ratio of the γ 'phase changes. The aspect ratio (ασ) in the case of a stress load increases (raft), but the aspect ratio (α ₀ ) in the case of no load decreases. The crafting ratio Φ (ασ / α ₀ ), which is the ratio between the aspect ratio with stress load and the aspect ratio without stress load, is a straight line on a semilogarithmic graph as indicated by a black circle in the figure.

This straight line can be expressed by equation (2). _{Pt / tr} = _Ptr + log (t / tr) (T + 273) and Φ = ^{Ct / tr} (2) where _{Pt / tr} : creep rupture life ratio (t / tr) LMP P _tr : LMP when t / tr = 1 LMP = (20 + logtr) (T + 273) × 10 ⁻³ T: hysteresis temperature (° C.) Φ: aspect ratio of the γ ′ phase (with stress load) / (stress load) Ratio C: maximum value of Φ depending on stress (LMP) (t / tr =
1)

A procedure for estimating the metal temperature T and the creep rupture life ratio t / tr of a high-temperature long-term material based on the γ 'phase change based on the above experimental data will be described with reference to FIGS. The procedure for estimating the metal temperature T of high-temperature long-term materials is as follows:
It is as follows. First, a scanning electron microscope (SEM) is used to observe the γ 'phase in a plane perpendicular to the stress direction and a plane parallel to the stress direction at a high magnification of about 5000 times, and observe the major axis a of the γ' phase in a plane perpendicular to the stress direction (no stress applied). And the minor axis b, and the major axis a ′ and minor axis b ′ of the γ ′ phase on the plane parallel to the stress direction (with stress applied).

In the image processing of the γ ′ phase, the average value d of the circle equivalent diameter of the γ ′ phase and the raft ratio Φ with / without the stress load of the aspect ratio of the γ ′ phase are obtained. gamma 'an average value of equivalent-circle diameters of phase d is in the measured gamma' an average value d of the circle equivalent diameter of major axis and minor axis of the phase.

The metal temperature T is estimated by using the average value d of the equivalent circle diameter of the γ ′ phase obtained as described above, and from the d- LMP diagram of FIG. 6 which is the experimental data to be evaluated, for the sample of FIG. Obtained the following equation. Here, the above d- LMP diagram and equation (1) are calibration curves obtained in advance from known samples of the temperature / time history. To estimate the metal temperature T, use time t
Needs to be known. Since the d change of the γ 'phase does not depend on the stress, the metal temperature T may be estimated by SEM observation of one of a plane perpendicular to and parallel to the stress direction.

LMP = 8.03 · log d +29.18 On the other hand, LMP is LMP = (T + 273) (20 + lo
gt) × 10 ⁻³ , the metal temperature T can be determined from both equations by the following equation. T = [(8.03 · logd + 29.18) / (20+
logt) × 10 ^-3 ] -273

The raft ratio Φ with / without a stress load of the aspect ratio of the γ ′ phase is represented by an aspect ratio σα (a ′ / b ′) of a γ ′ phase stress load and an aspect ratio σ ₀ without a stress load.
From (a / b), the ratio Φ (= σα / σ ₀ ) is obtained. In the estimation of the Φ-LMP relationship for each temperature and time, the average value d of the equivalent circle diameter of the γ ′ phase obtained in the above, the metal temperature T obtained in the above, and the Φ of the γ ′ phase obtained in the above are obtained in advance. -L
The relationship between MPs is obtained from equation (2), and the intersection of Φ and LMP is obtained by plotting as shown in the Φ-LMP diagram of FIG.

The creep rupture life ratio t / tr is t / tr of the estimated value of the Φ-LMP relation thus obtained.
Φ at tr = 1 becomes its maximum value, from which Φ = C
Draw the Φ-t / tr diagram of Figure 6 showing the relationship of ^{t / tr,} by applying the [Phi from this re-gamma 'phase observation, it is possible to estimate the creep rupture life ratio t / tr.

Alternatively, Φ-LMP for each metal temperature
In the relation, t / tr = 1, it is also possible to obtain the following equation and estimate t / tr <1 as shown in the Φ-LMP diagram of FIG. Φ ₁ = 1 + 4.14 × 10 ⁻¹³ · 10 ^0.4412 P1 P = P ₁ + log (t / tr) · [(T + 273) /
1000] Φ = 1 + (Φ ₁ −1) (t / tr)

[0021]

According to the present invention, by adopting the above-described structure, the change of the γ ′ phase due to long-time use at high temperature can be measured by using a calibration curve prepared in advance using an image processing apparatus and using a metal of a Ni-base heat-resistant alloy. Temperature estimation and creep rupture life ratio can be quickly and quantitatively estimated. As a result, for example, the reliability of the product can be ensured by taking measures to prevent the metal operating temperature and creep rupture of the gas turbine blade beforehand.

[Brief description of the drawings]

FIG. 1 is a photomicrograph showing that the Ni-base heat-resistant alloy used in Examples shows a sharp γ ′ phase before use at a high temperature.

FIG. 2 is a photomicrograph showing a rounded and coarse γ ′ phase obtained by adding a temperature / time history of LMP = 29.26 × 10 ³ to the γ ′ phase of FIG. 1;

FIG. 3 shows that the γ ′ phase of FIG. 1 gives a temperature / time history of LMP = 29.26 × 10 ³ and 5.2 kgf / mm ²
5 is a photomicrograph showing the state of the γ ′ phase when the stress of FIG.

FIG. 4 is a diagram showing the relationship between the average value d of the equivalent circle diameter of the γ ′ phase and LMP.

FIG. 5 shows an accept ratio α and a raft ratio Φ (= ασ /
FIG. 3 is a diagram showing a relationship between α ₀ ) and a creep rupture life ratio (t / tr).

FIG. 6 is a diagram for explaining a procedure for estimating a metal temperature and a creep rupture life ratio from a γ ′ phase change, and illustrates a procedure until γ ′ phase image processing is performed based on γ ′ phase SEM observation data. It is a figure for explaining.

FIG. 7 is a diagram for explaining a procedure for estimating a metal temperature and a creep rupture life ratio from a γ ′ phase change. FIG.
FIG. 6 is a diagram for explaining a procedure for estimating.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 17/00 G01M 19/00 G01N 3/32 G01N 33/20 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. The γ ′ of the metal structure in a Ni-base heat-resistant alloy
A method for evaluating a remaining life of a Ni-based heat-resistant alloy, comprising estimating a creep rupture life ratio by detecting a raft ratio of a phase. 2. A stress is applied to a Ni-base heat-resistant alloy sample whose temperature and time history is known, and the major axis and minor axis of the γ ′ phase are measured to obtain a circle-equivalent diameter, and the Larson-Miller parameter [LM]
A calibration curve between P = (T + 273) (C + logt)] and the circle equivalent diameter is obtained in advance, and the Ni to be evaluated is evaluated.
2. The method for evaluating the remaining life of a Ni-base heat-resistant alloy according to claim 1, wherein the metal temperature T is determined from the equivalent circle diameter of the γ 'phase of the base heat-resistant alloy. 3. A stress is applied to the Ni-base heat-resistant alloy sample to be evaluated, and the major axis and minor axis of the γ ′ phase are measured on a plane parallel to the load direction (stress-loaded plane) and a plane perpendicular to the loading direction (stress-free plane). ,
The aspect ratio (major axis / minor axis) of each surface is determined, and the raft ratio Φ (aspect ratio of the stress-loaded surface / aspect ratio of the surface without stress) is determined. 3. The method for evaluating the remaining life of a Ni-base heat-resistant alloy according to claim 2, wherein a creep rupture life ratio (history time t / creep rupture life tr) is determined from a relationship diagram of the parameter (LMP).